In metropolitan Washington, DC, an outbreak of aseptic meningitis in children was recognized in the summer and fall of 1972. Age-specific attack rates were highest in children less than 1 year of age. The incidence of cases showed two peaks: one in July and another in October. Coxsackievirus B5 was associated with cases occurring in July, August, and September, but was not implicated in the October cases. Seventy-six percent of the confirmed coxsackievirus B5 infections in aseptic meningitis patients occurred in infants less than 2 months old. Specific meningeal symptoms were less frequently observed in these young infants, although viral isolations were more common (13 of 15) compared to patients over 2 months of age (four of 19). Analysis of reported coxsackievirus B5 infections in Washington, DC, and the United States as a whole suggests a five- or six-year periodicity.